1. Field of the Invention
The present invention relates to a ratio communication apparatus such as an automobile telephone apparatus or the like and a method of controlling the apparatus, and more particularly to an apparatus for radio communication which is capable of accurately displaying the reception field strength and a method of controlling the apparatus.
2. Description of the Related Art
Automobile telephone apparatus are provided with a function for detecting the reception field strength for controlling a transmission output and determining whether or not the apparatus is in a usable area. Since it is helpful on the part of the users to know the reception field strength, the reception field strength is in many cases displayed on a display unit constituted by a liquid crystal display or the like.
In recent years, radio telephone apparatus of a type in which they are used in common as a portable telephone apparatus and a vehicle-mounted telephone apparatus have been developed and put on the market.
The radio telephone apparatus of this common use type comprises a main body mounted on the vehicle and a portable radio device which is used in a situation in which it is installed on the vehicle-mounted main body and i used by being removed from the main body as an independent radio telephone apparatus.
A control unit, a display unit and a key unit are provided on the portable radio device, and these units are used in common in either situation.
With such a common use-type radio telephone apparatus, however, depending on the situations where the portable radio device is used by being installed on the vehicle-mounted main body and where it is used independently, transmission routes leading from an antenna to various units of the apparatus differ. For this reason, when displaying the reception field strength on the display unit, there has been a problem in that, depending on the situations where the portable radio device is used by being installed on the vehicle-mounted main body and where it is used independently, the display value differs even though the reception field strength is actually the same.
In addition, when displaying the reception field strength on the liquid crystal display or the like, the display is usually effected on a digital basis. In the digital-basis display, threshold values for determining a plurality of stages set in correspondence with the reception field strength are stored in advance, and the stage of the reception field strength is determined on the basis of a comparison with the stored threshold values (reference values), and that stage is displayed on the liquid crystal display.
Conventionally, however, the aforementioned threshold values are fixedly stored in a ROM. Since the display of the reception field strength is dependent upon variations in the reception characteristics among apparatus, it is impossible to display the reception field strength accurately.